In recent years, with increases in the functionality and use of display devices, there has been an increasing need for improvements in touch panels and electromagnetic shielding members attached to the surfaces of display devices. In particular, since small devices such as smartphones and tablet terminals are used in the state where the users are close to the display devices, there has been an increasing demand for improvements in the viewability of display devices. For example, in the field of touch panels attached to the surfaces of display devices, instead of conductive transparent materials (ITO, IZO, and the like), which have been mainly used as wiring materials, use of copper wiring has been studied, the copper wiring being excellent in terms of cost balance and having a resistance one or two orders of magnitude lower than the resistances of ITO, IZO, and the like. In the case of using copper wiring, when the touch panel is viewed from the outside, the copper wiring is noticeable because of reflection by the surface of the copper wiring. This is prevented by subjecting the surface of copper wiring to blackening treatment. For the same purpose, also in the field of electromagnetic shielding members, the surfaces of copper wiring patterns are subjected to blackening treatment.
There are various production methods including blackening treatment during production processes of touch panels and electromagnetic shielding members. For example, there are the following known methods.
For example, Patent Literature 1 describes a method for producing a transparent conductive material, the method including a step of preparing a layered body in which a conductive pattern layer composed of a conductive composition containing silver particles and a binder resin is formed on a one surface side of a transparent substrate, and a step of forming a blackening layer by bringing the layered body into contact with a metal blackening treatment solution that is a hydrochloric acid solution containing tellurium dissolved, the hydrochloric acid solution having a tellurium concentration (concentration in terms of oxide) of 0.01 to 0.45 wt % and having a hydrochloric acid concentration of 0.05 to 8 wt %.
In addition, Patent Literature 2 describes a method in which a pretreatment such as degreasing or acid treatment of a conductive substrate is performed in a pretreatment tank; subsequently, metal is deposited on the conductive substrate in a plating tank; and the conductive substrate is further sequentially passed through a rinsing tank, a blackening treatment tank, a rinsing tank, an anticorrosive treatment tank, and a rinsing tank to thereby blacken the surface of the metal deposited on the conductive substrate.
Furthermore, Patent Literature 3 describes a method for producing a touch panel characterized by forming, by the following steps, a conductive mesh fine wire of an upper sensor electrode, the wire including a metal or alloy layer and a blackening layer formed on the layer: the method includes a step of forming a metal layer or alloy layer on a transparent substrate, a step of forming an electrode pattern in the metal layer or alloy layer, a step of forming a blackening layer over the metal layer or alloy layer, and a step of removing the blackening layer from non-electrode portions.